Project Summary Childhood obesity is a top public health concern. A large body of literature has supported a relationship between aspects of the built and social environment (BSE) and childhood obesity; however, the majority of evidence has been based on cross-sectional studies. Further, national studies of BSEs have been limited by several factors including: studying a narrow age range, utilizing less valid self-reported heights and weights, and/or not considering community programming and policies in concert with the effects of BSEs. Lastly, few studies have had sufficient sample sizes to examine differences by subgroups (e.g., race and ethnicity), which is critical for understanding the role of BSEs on health disparities. We have an unprecedented opportunity to address these gaps by capitalizing on the Healthy Communities Study: How Communities Shape Children's Health (HCS). The HCS was a $30 million study of 5,138 children and adolescents in grades K through 8 in 130 communities in the US. The main aim of the HCS was to identify characteristics of community programs and policies that impacted childhood obesity. As part of the parent HCS, children and their parent/guardian completed an in-person survey that included measured BMI. Retrospective participant BMI data (up to ten years) was obtained by medical chart review. In addition, information about current and historical community programs and policies was obtained from key informant interviews, secondary data sources, and document review. The proposed study, hereafter, referred to as the Healthy Communities Study ? Built and Social Environments (HCS-BSE), will expand the HCS by examining the effects of BSEs on childhood obesity. Specifically, we will obtain data on a broad range of current and historical BSE characteristics of the HCS communities (i.e., food availability, park availability, food prices, physical activity facilities, land use, street connectivity, and crime) and then spatially link these data to HCS participants. These unique data will permit the testing of numerous novel hypotheses, the results of which will significantly advance our understanding of the effects of BSEs on obesity across a geographically and racially diverse set of 130 communities. Further, these data will permit us to examine whether the relationship between community programs and policies and obesity depends on the BSEs in which these programs take place?a potential key moderating relationship that was not examined in the parent HCS study. The specific aims of the HCS-BSE study are to: 1) determine the longitudinal relationship between BSEs and BMI; 2) examine the moderating effects of individual (e.g., age, race, ethnicity) and community (e.g., urbanicity) characteristics on the relationship between BSEs and BMI; and 3) examine the moderating effects of BSEs on the relationship between community programs and policies and BMI. The HCS-BSE study is a cost-effective study that, when combined with the parent study, will be one of the most comprehensive childhood obesity studies in terms of its size, scale, quality of measures, and potential for scientific contributions to prevent childhood obesity.